Myxomycota: Plasmodial Slime Molds

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Myxomycota Plasmodial Slime Molds Dictyosteliomyc
ota Cellular Slime Molds
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F
UNGI (e.g., mushrooms, yeasts)
M
ICROSPORIDIA
M
ETAZOA (Animals)
Phylogeny Of Eukaryotes
D
ICTYOSTELIDAE
Slime molds
M
YXOGASTRIDAE
L
OBOSA
A
NGIOSPERMAE (Green Plants)
based on DNA sequence data
C
HLOROPHYCEAE
R
HODOPHYTA
(some water molds Irish potato famine Sudden Oak
Death)
G
LAUCOPHYTA
O
OMYCETES
P
HAEOPHYCEAE (Brown algae)
C
ILIOPHORA
A
PICOMPLEXA
K
INETOPLASTIDA
E
UGLENOIDEA
A
CRASIDAE
V
AHLKAMPFIIDAE
P
ARABASALLA
D
IPLOMONADIDA
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• typically uninucleate
• unicellular
• lacks a cell wall
• capable of changing shape
• lacking a definite form

amoeba
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• plasmodium
• multinucleate
• motile mass of protoplasm bounded by a plasma
• membrane but lacking a wall
• generally reticulate
• coenocytic
• pseudoplasmodium
• structure formed by the massing of separate
  myxamoebae
• myxamoebae do not fuse

plasmodium
pseudoplasmodium
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• Dictyosteliomycota cellular slime molds
• seldom see members of the group in nature
• fructifications are inconspicuous, delicate and
  ephemeral
• somatic phase is microscopic
• basic unit of structure is a uninucleate, naked,
  
• haploid amoeba (myxamoebae)
• feed by engulfing bacteria

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For an excellent website on Dictyostelium with
mpegs go to the following url http//www.zi.bio
logie.uni-muenchen.de/zoologie/dicty/dicty.html
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• Dictyosteliomycota cellular slime molds
• component amoebae do not fuse
• retain their individuality while cooperating as
  members of a
• well-organized community, pseudoplamodium
• Acrasin (cyclic AMP) pheromone responsible for
  aggregation
• of myxamoebae to form a mound stage

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• the mound stage of the pseudoplasmodium
  transforms into the
• mobile slug, or grex stage

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• grex results in the differentiation of
  myxamoebae occurs
• during formation of the sorocarp

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• Myxomycota true or plasmodial slime molds
• 500 described species
• phagotrophic nutrition
• life-cycle stages
• 1. three types of uninucleate single cells
• spore, myxamoeba, swarm cell

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• 2. multinucleate somatic phase known as a
  plasmodium
• moves and exhibits a reversible cytoplasmic
  streaming

3. resistant stage consisting of a sclerotium
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4. reproductive phase stationary sporophores
containing walled spores
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• Nutrition
• substrates upon which slime molds grow are of
  secondary
• importance
• fungi, bacteria, and protozoans are the source
  of nutrition for the
• phagotrophic myxamoeba stage
• moisture and temperature are important abiotic
  factors that
• contribute to the periodic appearance and
  seasonal nature
• of most species

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• Spores
• liberated from their sporophores by wind, water
  and the
• activities of animals
• generally globose with a thick cell wall
• surface may be smooth or ornamented
• typically contain a single haploid nucleus
• resistant to unfavorable conditions
• prolonged periods of desiccation
• some spores are capable of germinating after 75
  years

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• Spore Germination, Myxamoeba, and Swarm Cells.
• myxomycete spores probably germinate in rain
  water
• germination results in one or more myxamoebae or
  swarm cells
• myxamoebae convert into swarm cells
• reversible

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• swarm cells possess from 1 to 4 anteriorly
  attached whiplash
• flagella
• most possess one long prominent flagellum and a
• second shorter flagellum that is directed
  posteriorly
• absorbing dissolved food material and by
  ingesting fungi,
• bacteria, yeasts
• swarm cell can withdraw flagella and transform
  into
• a myxamoeba

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• When food is abundant and environmental
  conditions are
• favorable
• myxamoebae divide repeatedly
• give rise to a large population of cells
• Under unfavorable conditions
• myxamoebae encyst
• secrete a galactosamine wall to form microcysts
• When favorable conditions return
• microcysts germinate to produce either a
  myxamoeba or
• swarm cell

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• Formation of Zygotes and Plasmodia
• swarm cells and myxamoeba may function as
  gametes
• heterothallic strains fuse in pairs to form a
  zygote
• mating is unifactoral with multiple alleles
• resulting zygote is initially flagellate, swims,
  retracts flagella
• and tranforms into an amoeba-like cell
• as the zygote grows, its nucleus undergoes
  successive
• synchronous mitotic divisions without cytokinesis
• becomes transformed into a multinucleate
  plasmodium

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• plasmodium is a naked mass of protoplasm
• no cell wall
• enveloped by a gelatinous slime sheath that
  contains
• microfibrils
• sheath is shed as the plasmodium moves over the
  substrate
• inside the slime sheath is the plasma membrane
  that
• confines the cytoplasm
• various colors
• feed on bacteria, spores of fungi and plants,
  protozoa and
• decaying organic matter

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Sclerotia Under unfavorable environmental
conditions a plasmodium can become converted
into a sclerotium Irregular, hardened, resistant
mass capable of long periods of dormancy When
conditions are favorable, a plasmodium emerges
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Sporulation entire plasmodium of a myxomycete
is usually converted into one or more
sporophores
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• 1. Sporangium
• numerous stalked or sessile produced by
  plasmodium
• each sporangium has a unique peridium
• most common sporophore
• usually a few millimeters tall

Stemonitis
Metatrichium
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• Sporangium consists of the following parts
• /- hypothallus - secretion of the plasmodium on
  the substratum
• /- stalk,
• peridium (persistent or evanescent),
• /- columella - part of the stalk that continues
  into the spore-bearing
• region
• /- capillitium a system of secreted threads
  inside the sporophores,
• that are interspersed among the spores

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• 2. Aethalium
• fairly large, cushion-shaped sporophore
• derived from an entire plasmodium not
  differentiated into
• individual sporangia
• entire body is enclosed in a more or less
  continuous peridium

Lycogala
Fuligo
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• 3. Pseudoaethalium
• group of sporangia are crowded together
• appears to be a single sporophore
• individual sporangia, however, are not fused

Trichia
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• 4. Plasmodiocarp
• similar to a stalkless sporangium
• retains the morphology of the plasmodium
• protoplasm accumulates in some of the main veins
  of
• the plasmodium and develops into a sporophore

Hemitrichia